"""DB connection, session management, and migration runner (spec §8.1 rules 5 & 9)."""

import os
import re
import sqlite3
from pathlib import Path

from sqlalchemy import create_engine
from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker

DATABASE_URL = os.environ.get("CALCOUNT_DATABASE_URL", "sqlite:///./calcount.db")

engine = create_engine(
    DATABASE_URL,
    # Required for SQLite with FastAPI's threadpool handlers (spec §8.1 rule 4)
    connect_args={"check_same_thread": False},
)
SessionLocal = sessionmaker(bind=engine, autoflush=False, expire_on_commit=False)


class Base(DeclarativeBase):
    pass


def get_db():
    """One DB session per request (spec §8.1 rule 5)."""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


MIGRATIONS_DIR = Path(__file__).parent / "migrations"


def run_migrations(db_path: str | None = None) -> None:
    """Apply numbered SQL migrations in order, tracked in schema_migrations.

    Migrations from day one (spec §8.1 rule 9): never hand-edit the database;
    every schema change is a new numbered file.
    """
    if db_path is None:
        # Derive the SQLite file path from the engine URL
        db_path = engine.url.database
        if db_path in (None, ":memory:"):
            raise RuntimeError("run_migrations requires a file-backed SQLite database")

    conn = sqlite3.connect(db_path)
    try:
        conn.execute(
            "CREATE TABLE IF NOT EXISTS schema_migrations ("
            "  version INTEGER PRIMARY KEY,"
            "  applied_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ','now'))"
            ")"
        )
        applied = {row[0] for row in conn.execute("SELECT version FROM schema_migrations")}

        for path in sorted(MIGRATIONS_DIR.glob("*.sql")):
            match = re.match(r"(\d+)", path.name)
            if not match:
                continue
            version = int(match.group(1))
            if version in applied:
                continue
            conn.executescript(path.read_text())
            conn.execute("INSERT INTO schema_migrations (version) VALUES (?)", (version,))
            conn.commit()
    finally:
        conn.close()